Table 1.
Landmarks and definitions used to describe the cranio-cervical and pharyngeal/hyoid variables
| Reference point | Definition |
|---|---|
| Aa | Outermost point of the anterior arch of the atlas |
| Pa | Outermost point of the posterior arch of the atlas |
| C2a | Anteroinferior point of the second cervical vertebra |
| C3a | Anteroinferior point of the third cervical vertebra |
| C2pi | Posteroinferior point of the second cervical vertebra |
| C3pi | Posteroinferior point of the third cervical vertebra |
| C4pi | Posteroinferior point of fourth cervical vertebra |
| C2 ps | Posterosuperior point of the second cervical vertebra |
| APW2 | Intercept of the posterior pharyngeal wall co-linear with PPW2 |
| APW3 | Intercept of the posterior pharyngeal wall co-linear with PPW3 |
| PPW2 | Intercept of the posterior pharyngeal wall co-linear with C2pi and C2a |
| PPW3 | Intercept of the anterior pharyngeal wall co-linear with C3pi and C3a |
| HYa | Anterosuperior point of the hyoid bone |
| HYp | Posterosuperior point of the hyoid bone |
| N | Nasion: the most anterior point of the frontonasal suture |
| S | Sella: centre of sella turcica (pituitary fossa of the sphenoid bone) |
| Planes/distances | |
| AT | Line taken through points Aa and Pa |
| NSL | Line taken through the nasion and the sella |
| AT | Line through the points Aa and Pa |
| Hyoid plane | Line through points HYa and HYp |
| HY/AP | Perpendicular distance (mm) between HYa and vertical line through S |
| HY/VER | Vertical distance (mm) between HYa and NSL |
| PPW2– APW2 | Distance (mm) between PPW2 and APW2 |
| PPW3–APW3 | Distance (mm) between PPW2 and APW3 |
| HOR | Horizontal line perpendicular to the true vertical |
| VER | With reference to the true vertical |